Phase Modulation Device

ABSTRACT

The phase modulation device includes an image data generator, a gradation data generator, an adjustment voltage controller, and a reflective liquid crystal element. The image data generator generates image data corresponding to a distribution. of phase change amount or a distribution of phase velocity. The gradation data generator generates gradation data corresponding to each pixel. The reflective liquid crystal element includes a pixel region having a plurality of pixel blocks, and an adjustment electrode. The adjustment voltage controller applies an adjustment voltage having a same voltage value as a driving voltage applied to a pixel electrode of the pixel block adjacent to the adjustment electrode.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation of PCT Application No. PCT/JP2018/037208, filed on Oct. 4, 2018, and claims the priority of Japanese Patent Application No. 2017-197404, filed on Oct. 11, 2017, the entire contents of both of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a phase modulation device using a liquid crystal element.

In recent years, in an optical communication field, an optical network system formed in an annular shape and an optical wavelength division multiplexing communication system have been proposed in order to cope with a rapidly increasing amount of information. A reconfigurable optical add/drop multiplexer (ROADM) device is used that can perform branching or insertion of an optical signal in these optical communication systems without, relaying conversion to an electrical signal. In the ROADM device, as an optical switching device, a wavelength selective switch (WSS) device is used. As an optical switching element in the WSS device, a micro electro mechanical systems (MEMS) mirror, and a reflective liquid crystal element, for example, a liquid crystal on silicon (LCOS) element or the like are used.

The LCOS element is a reflective liquid crystal element having a pixel region in which a plurality of reflective pixel electrodes are arranged in a horizontal direction and a vertical direction. A refractive index of a liquid crystal on each pixel electrode changes by controlling a voltage applied to the liquid crystal for each pixel electrode. The phase velocity of the signal light is controlled for each pixel by changing the refractive index of the liquid crystal on each pixel.

The LCOS element can incline a wavefront of the signal light by changing the phase velocity stepwise for each pixel. The LCOS element can control an inclination angle of the wavefront of the signal light according to a rate of change of the phase velocity. That is, the LCOS element functions as a phase modulation element that reflects the signal light in a predetermined direction by changing the phase velocity for each pixel.

The MEMS mirrors are required corresponding to the number of wavelength bands of the signal light. For that reason, when the wavelength band of signal light or the number thereof is changed, the MEMS mirror has to be newly manufactured in accordance with the changed contents.

In contrast, the LCOS element can arbitrarily divide the pixel region into a plurality of pixel blocks and can control each pixel block. Therefore, when the wavelength band of signal light or the number thereof is changed, the pixel block can be reconfigured in accordance with the changed content, and thus it is not necessary to newly manufacture a liquid crystal element. That is, the LCOS element is superior in variable grid property than the MEMS mirror. In Japanese Unexamined Patent Application Publication No. 2016-143037, an example of the phase modulation device using the LCOS element is described.

SUMMARY

Usually, a peripheral region that does not contribute to phase modulation is formed outside a pixel region adjacent to the pixel region. Disclination may occur due to a potential difference between the pixel region and the peripheral region. Disclination means that liquid crystal molecules tilt in a direction different from the intended direction due to a potential difference. If the potential difference is large, the lateral electric field becomes large, so that disclination is likely to occur or the generation area is widened.

Since the signal light is reflected at an inclination angle different from the target inclination angle due to the influence of disclination, the crosstalk incident on an output port different from the target output port occurs.

An aspect of one or more embodiments provides a phase modulation device including: an image data generator configured to generate image data corresponding to a distribution of phase change amount or a distribution of phase velocity based on information data; a gradation data Generator configured to generate gradation data corresponding to each pixel based on the image data; an adjustment voltage controller configured to generate an adjustment voltage based on the gradation data; and a reflective liquid crystal element to which the gradation data and the adjustment voltage are applied; wherein the reflective liquid crystal element includes: a pixel region in which a plurality of pixel electrodes are arranged, and a driving voltage of a sawtooth waveform voltage pattern corresponding to the gradation data is applied; and a first adjustment electrode adjacent to the pixel region in a first direction in which the voltage pattern is repeated, the pixel region comprises a plurality of pixel blocks configured to modulate the phase of signal light incident on the pixel region based on the voltage pattern, and to change a wavefront of the signal light, and the adjustment voltage controller applies an adjustment voltage having a same voltage value as a driving voltage applied to a pixel electrode of a pixel block adjacent to the first adjustment electrode, to the first adjustment electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a phase modulation device according to one or more embodiments.

FIG. 2 is a top view illustrating an example of a reflective liquid crystal element.

FIG. 3 is a cross-sectional view of the reflective liquid crystal element taken along line A-A in FIG. 2.

FIG. 4 is a cross-sectional view of the reflective liquid crystal element taken along line B-B in FIG. 2.

FIG. 5 is a diagram illustrating phase modulation of the signal light by a reflective liquid crystal element.

FIG. 6A is a diagram illustrating a driving voltage applied to a pixel electrode.

FIG. 6B is a diagram illustrating a refractive index of a liquid crystal on the pixel electrode.

FIG. 7 is a diagram illustrating a relationship between a pixel block in a pixel region and an adjustment electrode.

FIG. 8A is a diagram illustrating an example of a voltage pattern of a driving voltage along C1-C2 in FIG. 7.

FIG. 8B is a diagram illustrating an example of a voltage pattern of a driving voltage along D1-D2 in FIG. 7.

DETAILED DESCRIPTION

A phase modulation device according to one or more embodiments will be described with reference to FIG. 1. A phase modulation device 1 includes an image data generator 2, a gradation data generator 3, an adjustment voltage controller 5, and a reflective liquid crystal element 10. The reflective liquid crystal element 10 is an LCOS element, for example. Hereinafter, the reflective liquid crystal element 10 is referred to as an LCOS element 10.

Information data JD is input to the image data generator 2. The information data JD includes a parameter indicating a relationship between positions of an input port and an output port of signal light and an angle of reflected light with respect to incident light in the signal light, and a parameter related to a wavelength band of the signal light, that is, a distribution of phase change amount that realizes a desired reflected light angle. The phase change amount is the lead or lag of the phase of the reflected light with respect to the phase of the incident light, and corresponds to the distribution of phase velocity. The signal light emitted from a predetermined input port is phase-modulated by the phase modulation device 1 and enters a target output port.

The image data generator 2 sets the distribution of phase change amount based on the information data JD. The image data generator 2 generates image data DD based on the distribution of phase change amount or the distribution of phase velocity, and outputs the generated image data DD to the gradation data generator 3. The gradation data generator 3 generates gradation data DS corresponding to each pixel in the LCOS element 10 of the image data DD, and outputs the gradation data DS to the LCOS element 10 in accordance with the timing of writing to each pixel. A driving voltage corresponding to this gradation is generated in the LCOS element 10 and applied to the liquid crystal. The gradation data generator 3 outputs the gradation data DS to the adjustment voltage controller 5.

A configuration example of the LCOS element 10 will he described with reference to FIGS. 2 to 4. The LCOS element 10 includes a driving substrate 20, a transparent substrate 30, liquid crystals 11, and a sealing material 12. The driving substrate 20 includes a pixel region 21, an alignment film 22, a connection terminal 23, and an adjustment electrode 40. In the pixel region 21, a plurality of reflective pixel electrodes 24 are arranged in the horizontal and vertical directions. One pixel electrode 24 constitutes one pixel.

The alignment film 22 is formed at least on the pixel region 21. The connection terminal 23 is formed on the outer peripheral portion of the driving substrate 20, receives the gradation data DS from the gradation data generator 3, and receives a timing control signal from the outside. The connection terminal 23 is also connected to a power supply and the like from the outside.

The adjustment electrode 40 is formed around the pixel region 21 and adjacent to the pixel region 21. The alignment film 22 is formed on the pixel region 21 and the adjustment electrode 40. The connection terminal 23 is formed on the outer peripheral portion of the driving substrate 20 and connected to the adjustment voltage controller 5 illustrated in FIG. 1.

The transparent substrate 30 includes a transparent electrode 31 and an alignment film 32. The alignment film 32 is formed on the transparent electrode 31. The driving substrate 20 and the transparent substrate 30 are bonded to each other with a gap by the sealing material 12 so that the pixel electrode 24 and the transparent electrode 31 face each other.

The sealing material 12 is formed in an annular shape along the outer peripheral portion of the adjustment electrode 40. In FIGS. 2 to 4, the sealing material 12 is formed in a region outside the adjustment electrode 40, but may be formed over a part of the region of the adjustment electrode 40. The liquid crystals 11 are filled in a gap between the driving substrate 20 and the transparent substrate 30 and are sealed by the sealing material 12. An anti-reflection film 33 may be formed on the surface opposite to the surface on which the transparent electrode 31 of the transparent substrate 30 is formed.

A semiconductor substrate (a silicon substrate, for example) can be used as the driving substrate 20. A drive circuit for driving each pixel is formed on the driving substrate 20. As a material of the pixel electrode 24, the connection terminal 23, and the adjustment electrode 40, a metal material containing aluminum as a main component can be used.

As the transparent substrate 30, a non-alkali glass substrate or a quartz glass substrate can be used. As a material of the transparent electrode 31, Indium Tin Oxide (ITO) can be used. A dielectric film may be formed above and below the ITO film. As the sealing material 12, an ultraviolet curable resin, a thermosetting resin, or a resin that is cured by using both ultraviolet light and heat can be used. As the anti-reflection film 33, a dielectric multilayer film can be used.

The phase modulation of the signal light by the LCOS element 10 will be described with reference to FIGS. 5, 6A, and 6B. In order to make the description easy to understand, a case where a pixel block 25 is configured by three pixel electrodes 24 will be described. Usually, the pixel block 25 has a configuration in which three or more pixel electrodes 24 are arranged in the horizontal direction and the vertical direction, respectively. In order to distinguish each pixel electrode 24, it is assumed to be pixel electrodes 24 a, 24 b, and 24 c from the left.

Based on the image data DD corresponding to the distribution of phase change amount (distribution of phase velocity) generated by the image data generator 2 illustrated in FIG. 1, different driving voltages DVa, DVb, and DVc are applied to the pixel electrodes 24 a, 24 b, and 24 c as illustrated in FIG. 6A. Actually, the driving voltages DVa, DVb, and DVc applied to the liquid crystals 11 are voltages applied between the pixel electrodes 24 a, 24 b, and 21 c and the transparent electrode 31. Since the liquid crystals 11 have anisotropy in the refractive index and the dielectric constant of the constituent molecules, the refractive index changes by changing the tilt of the molecules according to the applied voltage.

Therefore, as illustrated in FIG. 6B, the liquid crystals 11 on the pixel electrode 24 a have a first refractive index na, the liquid crystals 11 on the pixel electrode 24 b have a second refractive index nb, and the liquid crystals 11 on the pixel electrode 24 c have a third refractive index nc (na>nb>nc). The refractive indexes na to nc are average refractive indexes of the liquid crystals 11 on the pixel electrodes 24 a to 24 c.

Signal light SL output from the input port is incident on the pixel block 25 in a state of linearly polarized light of p-polarized light or s-polarized light. The alignment films 22 and 32 illustrated in FIG. 3 are formed so that the deflection direction of the signal light SL and the alignment direction of the liquid crystals 11 are the same. The alignment direction is a direction ire which the liquid crystals 11 in the vicinity of the alignment film 22 are inclined, for example. The direction in which the liquid crystals 11 in the vicinity of the alignment film 32 are inclined may be the alignment direction.

By making be deflection direction of the signal light SL and the alignment direction of the liquid crystal 11 the same, it is possible to suppress attenuation of the signal light SL caused by the modulation of linearly polarized light into elliptically polarized light and the p-polarized light having an s-polarized light component or the s-polarized light having a p-polarized light component, and the signal light SL can be efficiently reflected.

Pa, pb, and pc illustrated in FIG. 5 schematically show a difference in the phase velocity caused by a difference in the refractive index of the liquid crystals 11 on the pixel electrodes 24 a, 24 b, and 24 c. A WF illustrated in FIG. 5 schematically illustrates a wavefront of the signal light SL. The wavefront WF is a surface in which the phases of the signal light SL are aligned. The phase change amount or phase velocity of the signal light SL increases stepwise from the pixel electrode 24 a toward the pixel electrode 24 c. As a result, the wavefront WF of the signal light SL can be changed (inclined).

By the driving voltages DVa, DVb, and DVc, an inclination angle θ of the wavefront WF can be increased by increasing the difference in the refractive index of the liquid crystal 11 on the pixel electrodes 24 a, 24 b, and 24 c and increasing the difference in phase change. The inclination angle θ of the wavefront WF can be reduced by reducing the difference in the refractive index of the liquid crystals 11 on the pixel electrodes 24 a, 24 b, and 24 c, and reducing the difference in the phase change. The inclination angle θ corresponds to an angle formed by the wavefront WF of the signal light SL and the perpendicular lines of the pixel electrodes 24 a, 24 b, and 24 c. The inclination angle θ of the wavefront WF can be changed by changing the number of pixel electrodes 24.

The signal light SL is reflected by the pixel electrodes 24 a, 24 b, and 24 c with the wavefront WF having a predetermined inclination angle θ based on the image data DD generated by the image data generator 2. Therefore, the LCOS element 10 can reflect the signal light SL in a predetermined direction by changing the phase velocity of the signal light SL stepwise for each pixel based on the image data DD.

The LCOS element 10 can control the inclination angle θ of the wavefront WF of the signal light SL according to the rate of change of the phase velocity. That is, the LCOS element 10 functions as a phase modulation element that changes the phase velocity for each pixel and reflects the signal light SL in a predetermined direction. When the LCOS element 10 controls the inclination angle θ of the wavefront WF of the signal light SL, the signal light SL is incident on a target output port.

The relationship between the pixel block 25 in the pixel region 21 and the adjustment electrode 40 will be described with reference to FIGS. 7, 8A, and 8B. FIG. 7 illustrates a configuration when the pixel region 21 illustrated in FIG. 2 is divided into four pixel blocks 25. The signal light SL enters each pixel block 25.

The range and position of the pixel block 25 are determined based on the information data JD. The pixel block 25 is configured to include an incident area 26 on which the signal light SL incident. The incident area 26 is determined based on the spot diameter, spot shape, incident position accuracy, and the like of the signal light SL. The LCOS element 10 can reconfigure the pixel block 25 in accordance with the changed contents of the information data JD.

The LCOS element 10 can control the inclination angle θ of the wavefront WF of the signal light SL for each pixel block 25 based on the image data DD generated by the image data generator 2. In order to distinguish each pixel block 25, the upper left pixel block 25 is referred to as a pixel block 25 a, the lower left pixel block 25 is referred to as a pixel block 25 b, the upper right pixel block 25 is referred to as a pixel block 25 c, and the lower right pixel block 25 is referred to as a pixel block 25 d.

The signal light SL of different wavelength bands can be made incident on the pixel blocks 25 a to 25 d. The LCOS element 10 can apply driving voltages of different voltage patterns to the pixel blocks 25 a to 25 d based on the image data DD.

A case where a driving voltage DV is controlled by the amplitude of the voltage value will be described with reference to FIGS. 8A and 8B. FIG. 8A illustrates a voltage pattern of the driving voltage DV of the continuous pixels along C1-C2 of the pixel block 25 a illustrated in FIG. 7. Although the same voltage pattern as that of the pixel block 25 a is illustrated in the pixel block 25 c in FIG. 7, a driving voltage DV having a different voltage pattern can be applied.

FIG. 8B illustrates a voltage pattern of the driving voltage DV of the continuous pixels along D1-D2 of the pixel block 25 c illustrated in FIG. 7. Although the same voltage pattern as that of the pixel block 25 c is illustrated in the pixel block 25 d in FIG. 7, a driving voltage DV having a different voltage pattern can be applied.

As illustrated in FIGS. 8A and 8B, the driving voltage DV has a sawtooth waveform voltage pattern. Since the voltage is actually a voltage for each continuous pixel, the voltage has a stepped shape, but here, the voltage is illustrated in a sawtooth shape. In the pixel blocks 25 a to 25 d illustrated in FIG. 7, dark portions correspond to low voltage portions of the voltage pattern of the driving voltage DV illustrated in FIG. 8A or 8B, and bright portions correspond to high voltage portions. Since the voltage pattern illustrated in FIG. 8A has a larger amplitude of the voltage value than the voltage pattern illustrated in FIG. 8B, the inclination angle θ of the wavefront WF of the signal light SL increases.

Here, it is assumed that the liquid crystals 11 are a horizontally aligned liquid crystal material, that is, a liquid crystal material having a positive dielectric anisotropy. In a horizontally aligned liquid crystal, the refractive index increases as the voltage amplitude is increased. In the case of a vertically aligned liquid crystal material, that is, a liquid crystal material having a negative dielectric anisotropy, the refractive index is lowered by increasing the voltage amplitude. Moreover, the refractive index and the anisotropy of the refractive index differ depending on the liquid crystal material. In addition, the resulting phase change amount differs depending on the thickness of the liquid crystal layer.

The voltage pattern of the driving voltage DV is set based on the image data DD generated by the image data generator 2. Therefore, the ranges and positions of the pixel blocks 25 a to 25 d are determined based on the information data JD, the incident signal light SL is phase-modulated based on the voltage pattern of the driving voltage DV, thereby changing (inclining) the wavefront WF of the signal light SL. The control by a PSM method in which the driving voltage DV is controlled by a pulse width or the number of pulses is also effective. In this case, the vertical axis in FIGS. 8A and 8B corresponds to the integration time of the applied pulse of the driving voltage DV in one frame.

In order to distinguish each adjustment electrode 40, with respect to the pixel region 21, the adjustment electrode 40 adjacent to the first side (upper side in FIG. 7) in a first direction (vertical direction in FIG. 7) in which the sawtooth waveform voltage pattern is repeated is referred to as an adjustment electrode 41 (first adjustment electrode), and the adjustment electrode 40 adjacent to the second side (lower side in FIG. 7) opposite to the first side in the first direction is referred to as an adjustment electrode 42 (third adjustment electrode).

With respect to the pixel region 21, the adjustment electrode 40 adjacent to the third side (left side in FIG. 7) in the second direction (left-right direction in FIG. 7) orthogonal to the first direction is referred to as an adjustment electrode 43 (second adjustment electrode), and the adjustment electrode 40 adjacent to the fourth side (right side in FIG. 7) opposite to the third side in the second direction is referred to as an adjustment electrode 44 (fourth adjustment electrode).

A blank area 50 that does not contribute to phase modulation may be formed between the pixel blocks 25. FIG. 7 illustrates a case where the blank area 50 is formed between the pixel blocks 25 a and 25 c and the pixel blocks 25 b and 25 d. The blank area 50 may be formed between the pixel blocks 25 a and 25 b and the pixel blocks 25 c and 25 d, or the blank area 50 may be formed on both of them.

The adjustment voltage controller 5 can drive the adjustment electrodes 41 to 44 with a voltage signal synchronized with the transparent electrode 31 based on the gradation data DS.

A case where the driving voltage DV is controlled by the amplitude of the voltage value will be described. The adjustment voltage controller 5 applies, to the adjustment electrode 41 adjacent to the pixel electrodes 24 of the pixel blocks 25 a and 25 c, an adjustment voltage AV having the same voltage value as the driving voltage DV applied to the pixel electrodes 24 of the pixel blocks 25 a and 25 c so that the potential difference between the adjustment electrode 41 and the transparent electrode 31 is the same as the potential difference between the pixel electrodes 24 of the pixel blocks 25 a and 25 c and the transparent electrode 31.

The adjustment voltage controller 5 applies, to the adjustment electrode 42 adjacent to the pixel electrodes 24 of the pixel blocks 25 b and 25 d, an adjustment voltage AV having the same voltage value as the driving voltage DV applied to the pixel electrodes 24 of the pixel blocks 25 b and 25 d so that the potential difference between the adjustment electrode 42 and the transparent electrode 31 is the same as the potential difference between the pixel electrodes 24 of the pixel blocks 25 b and 25 d and the transparent electrode 31.

For example, the voltage value of the driving voltage DV applied to the pixel electrode 24 adjacent to the adjustment electrode 41 in the pixel blocks 25 a and 25 c is assumed to be va, and the voltage value of the driving voltage UV applied to the pixel electrode 24 adjacent to the adjustment electrode 42 in the pixel blocks 25 b and 25 d is assumed to be vb (va<vb). The adjustment voltage controller 5 applies an adjustment voltage AV having the voltage value va to the adjustment electrode 41, and applies an adjustment voltage AV having the voltage value vb to the adjustment electrode 42.

Therefore, the potential difference between the pixel blocks 25 a and 25 c and the adjustment electrode 41 and the potential difference between the pixel blocks 25 b and 25 d and the adjustment electrode 42 can be reduced, so that the occurrence of disclination can be suppressed.

The adjustment voltage controller 5 applies, to the adjustment electrode 43 adjacent to the pixel electrodes 24 of the pixel blocks 25 a and 25 b, an adjustment voltage AV having an average voltage value or an intermediate voltage value between the maximum voltage value and the minimum voltage value of the driving voltage DV applied to the pixel electrode 24 adjacent to the adjustment electrode 43. The adjustment voltage controller 5 applies, to the adjustment electrode 44 adjacent to the pixel electrodes 24 of the pixel blocks 25 c and 25 d, an adjustment voltage AV having an average voltage value or an intermediate voltage value between the maximum voltage value and the minimum voltage value of the driving voltage DV applied to the pixel electrode 24 adjacent to the adjustment electrode 44.

Therefore, the maximum potential difference between the pixel blocks 25 a and 25 b and the adjustment electrode 43 and the maximum potential difference between the pixel blocks 25 c and 25 d and the adjustment electrode 44 can be reduced, so that occurrence of disclination can be suppressed.

When the driving voltage UV is controlled by a Pulse Width Modulation (PWM) method, the adjustment voltage controller 5 associates the gradation data in the pixel region 21 with the gradation data in the adjustment electrodes 41 to 44 by the PWM method to generate an adjustment voltage AV and applies the generated adjustment voltage AV to the adjustment electrodes 41 to 44.

The adjustment voltage controller 5 synchronizes the voltage applied to the transparent electrode 31 so that the potential difference between the adjustment electrode 41 and the transparent electrode 31 is the same as the potential difference between the pixel electrodes 24 of the pixel blocks 25 a and 25 c and the transparent electrode 31, in the adjustment electrode 41, and applies an adjustment voltage AV having the same voltage pattern as the driving voltage DV applied to the pixel electrodes 24 of the pixel blocks 25 a and 25 c adjacent to the adjustment electrode 41.

The adjustment voltage controller 5 synchronizes the voltage applied to the transparent electrode 31 so that the potential difference between the adjustment electrode 42 and the transparent electrode 31 is the same as the potential difference between the pixel electrodes 24 of the pixel blocks 25 b and 25 d and the transparent electrode 31, in the adjustment electrode 42, and applies an adjustment voltage AV having the same voltage pattern as the driving voltage DV applied to the pixel electrodes 24 of the pixel blocks 25 b and 25 d adjacent to the adjustment electrode 42.

The adjustment voltage controller 5 generates an adjustment voltage AV to have an average voltage value or an intermediate voltage value between the maximum voltage value and the minimum voltage value of the driving voltage DV applied to the pixel electrodes 24 of the pixel blocks 25 a and 25 b adjacent to the adjustment electrode 43, and applies the generated adjustment voltage AV to the adjustment electrode 43 in synchronization with the voltage applied to the transparent electrode 31.

The adjustment voltage controller 5 generates an adjustment voltage AV to have an average voltage value or an intermediate voltage value between the maximum voltage value and the minimum voltage value of the driving voltage DV applied to the pixel electrodes 24 of the pixel blocks 25 c and 25 d adjacent to the adjustment electrode 44, and applies the generated adjustment voltage AV to the adjustment electrode 44 in synchronization with the voltage applied to the transparent electrode 31.

Therefore, the potential difference between the pixel blocks 25 a and 25 b and the adjustment electrode 43 and the potential difference between the pixel blocks 25 c and 25 d and the adjustment electrode 44 can be reduced, so that the occurrence of disclination can be suppressed.

In accordance with the phase modulation device 1 according to one or more embodiments, since the potential difference between the pixel region 21 and the peripheral region can be reduced by the adjustment electrode 40, the occurrence of disclination due to the potential difference between the pixel region 21 and the peripheral region can be suppressed.

The present invention is not limited to one or more embodiments described above, and various modifications may be made thereto without departing from the scope of the present invention. 

What is claimed is:
 1. A phase modulation device comprising: an image data generator configured to generate image data corresponding to a distribution of phase change amount or a distribution of phase velocity based on information data; a gradation data generator configured to generate gradation data corresponding to each pixel based on the image data; an adjustment voltage controller configured to generate an adjustment voltage based on the gradation data; and a reflective liquid crystal element to which the gradation data and the adjustment voltage are applied; wherein the reflective liquid crystal element comprises: a pixel region in which a plurality of pixel electrodes are arranged, and a driving voltage of a sawtooth waveform voltage pattern corresponding to the gradation data is applied; and a first adjustment electrode adjacent to the pixel region in a first direction in which the voltage pattern is repeated, the pixel region comprises a plurality of pixel blocks configured to modulate the phase of signal light incident on the pixel region based on the voltage pattern, and to change a wavefront of the signal light, and the adjustment voltage controller applies an adjustment voltage having a same voltage value as a driving voltage applied to a pixel electrode of a pixel block adjacent to the first adjustment electrode, to the first adjustment electrode.
 2. The phase modulation device according to claim 1, wherein the reflective liquid crystal element further comprises a second adjustment electrode adjacent to the pixel region in a second direction orthogonal to the first direction, and the adjustment voltage controller applies an adjustment voltage of an average voltage value of a driving voltage applied to a pixel electrode of a pixel block adjacent to the second adjustment electrode, to the second adjustment electrode.
 3. The phase modulation device according to claim 1, wherein the reflective liquid crystal element further comprises a second adjustment electrode adjacent to the pixel region in second direction orthogonal to the first direction, and the adjustment voltage controller applies an adjustment voltage of an intermediate voltage value between a maximum voltage value and a minimum voltage value of a driving voltage applied to a pixel electrode of a pixel block adjacent to the second adjustment electrode, to the second adjustment electrode.
 4. The phase modulation device according to claim 1, wherein the information data includes a parameter indicating a relationship between positions of an input port and an output port of the signal light and an angle of reflected light with respect to incident light in the signal light, and a parameter of a wavelength band of the signal light. 